One approach to improving the efficiency of solar cells is by employing micro- or nano-structures to enhance light collection. Such structures can be used to redirect sunlight incident over a wide range of incident angles into guided optical modes in the semiconductor. This makes the direction of light propagation orthogonal to the direction relevant to carrier diffusion, allowing large absorption efficiency and large carrier collection efficiency in the same device.
For certain choices of materials and structures, incident light can also excite surface plasmon resonances (SPRs) in metal-semiconductor interfaces in the solar cell. SPRs increase absorption by acting as sub-wavelength antennas with a plasmonic nearfield that is coupled to the semiconductor layer. Moreover, SPRs enhance the coupling of energy into in-plane photonic as well as surface plasmonic modes.
In order for the improved efficiency and reduced material thickness of such cells to dramatically reduce the cost per watt of electricity generated from these cells, what is needed is a method for fabricating the nanostructure “textures” (i.e., grooves or ridges) that is low-cost, high-throughput and compatible with roll-to-roll processing techniques (i.e., can be integrated into standard high-volume solar-cell manufacturing processes). One way to efficiently scatter the wavelengths of light that make up the solar spectrum is with nanostructure textures that have at least one dimension similar or smaller to the wavelength of the incident light. Examples of such textures include grooves or ridges with height and/or depth of approximately 50-100 nm. A scalable, low-cost method to produce such textures is desirable.